Overload clutches are used extensively with automated machinery in single directional drive applications, such as with bottling and canning equipment, amusement rides, and car wash equipment, for example. They are also sometimes used in two-directional applications, such as with manufacturing equipment and parts assembly equipment.
Typically, overload clutches are utilized with a mechanical switch, such as a limit switch, mounted in close proximity to a detector plate carried by the overload clutch. That is, when an equipment jam is noted by the overload clutch, its spring-urged detent means will move, thereby expanding the clutch axially and moving the detector plate into physical engagement with the limit switch (e.g., roller, button or wire-type). Once such movement of the detector plate is sensed by the limit switch, it in turn sends a signal to shut down the drive motor, any reducer, and related equipment. Examples of such overload clutches are typified by the Torq-Guard (Trademark) of Commercial Cam Division of Emerson Electric Co., the assignee of the present invention. Other overload clutches are typied by U.S. Pat. Nos. 3,282,387, 3,546,897, 3,924,421, and 5,067,600, also owned by the assignee of the present invention, but many of these have steel detector plates.
Typically, the detector plates for such overload clutches, particularly for the less-to-moderate expense range type clutches as used in general single directional drive applications, are formed of a high grade engineering type of injection-moldable plastic material. Such plastic detector plates have been satisfactory for use with motion switches. However, more recently, there has been a need to use proximity switches with such overload clutches. Importantly, in use, proximity switches do not have or make physical contact with any detector plate structure. Rather, they sense motion of a metal surface moving towards (or away from) the proximity switch (depending in which condition the switch is set). Accordingly, movement of the typical injection-moldable plastic, i.e., non-metal, detector plate is simply not able to be "seen" by a proximity switch sensing device.
Various attempts have been made to solve this problem. One solution includes forming the detector plate as a solid steel piece; however, that approach is very costly and adds excessive, unneeded inertia forces to the overall overload clutch unit. Another prior art approach to this problem has been to simply rivet or otherwise fasten a metal disk to the injection-molded plastic detector plate. However, due to the high rpm's and significant inertia created (during the high speed stopping and starting of such overload clutches and related machinery), total failures of such riveted detector plates occurred. The detector plate pins were simply sheared off, whereby the detector plate no longer functioned with the clutch unit. Yet another prior attempt to solve this problem was, instead of making the detector plate out of injection-moldable plastic, to form it completely out of machined steel. However, such very heavy steel detector plates created unnecessary inertial problems due to the quick acceleration and deceleration of such overload clutch units.
Thus, there has been an industry need for an inexpensive, low inertia yet sturdy detector plate structure having one or more surfaces that could be "seen" by a proximity switch when the overload clutch caused movement of the detector plate during an overload condition.